氮沉降对干旱区凋落物分解机制及养分释放的影响

Changes in nitrogen deposition in response to global climate change are impacting carbon budgets in arid ecosystem. Litter decomposition is the key process in the carbon cycle, but it underlying mechanism of nitrogen deposition effects on decomposition remains poorly understood. In desert regions, the content of leaf chemical element is restricted by limited nutrient availability. Resent studies found that measured decomposition rates were typically much greater than predicted values, and poor litter quality was the determinant in surface litter decomposition in desert areas. This implies that stoichiometric balance between litter and consumer (microorganisms) may be a fundamental cause for high decomposition rate in desert ecosystems. Here, individual species and mixed-species litter contrasted C:N:P stoichiometry will be studied to asses how the stoichiometry traits of residues and the plant species composition affect the decomposition process, respectively. Meanwhile, we also studied the direct and indirect effects of nitrogen deposition on litter decomposition to get a better understanding how increased atmospheric N deposition would affect soil nutrient dynamics and C storage in desert ecosystems. This study will provide theoretical support for further understanding of the carbon accumulation and nutrient cycling of desert ecosystems.

大气氮沉降显著影响了干旱生态系统的C收支，但对荒漠植物凋落物分解的影响机制尚不清楚。本研究以原生荒漠植物单种及混合凋落叶为分解基质，研究物种组成和凋落物化学计量组成对分解过程和养分释放的影响，分析控制凋落物分解的内、外在因素，揭示荒漠区凋落物的分解与物种多样性的关系；同时，研究模拟氮沉降处理，对凋落物分解的直接效应和间接效应，揭示荒漠植物凋落物分解对大气氮沉降的响应过程，为完整构建荒漠生态系统碳、氮循环模型提供关键的理论依据。

大气氮沉降显著影响了干旱生态系统的C收支，但对荒漠植物凋落物分解的影响机制尚不清楚。本研究采用分解网袋法，以原生荒漠植物单种及混合凋落叶为分解基质，研究物种组成和凋落物化学计量组成对分解过程的影响，揭示凋落物分解与物种多样性的关系。同时，研究了外源氮添加对凋落物分解的直接效应和间接效应，揭示荒漠植物凋落物分解对大气氮沉降的响应过程。结果表明：（1）初始P含量和木质素含量是影响单种凋落物分解的关键因子；（2）多数混合凋落物不产生显著的非加和效应，相反，大多数混合凋落物显著影响了分解过程中的N、P释放；（3）初始化学计量组成不同的梭梭凋落物混合表现为正的非加和效应，且与初始C:N 和N含量存在显著相关关系；（4）氮沉降对单种凋落物及其混合物分解的直接效应较小，但各种凋落物的养分动态对大气氮沉降有不同的响应，且因物种和分解时间而异；（5）氮沉降通过改变凋落物质量对分解的间接作用显著，显著抑制梭梭凋落物的分解，延缓了其N、P养分向土壤系统的释放。可见，在温带荒漠，凋落物初始化学组成是预测凋落物分解的重要因素，适量的氮输入主要通过间接作用影响分解过程，未来气候变化下，植物物种组成的变化所引起的凋落物质量的改变将深刻影响荒漠生态系统的碳周转和养分循环。